Detectors used in known Time-of-Flight (TOF) mass spectrometers, as well as the position sensitive detectors used in imaging mass spectrometry and other applications which require detection of ions with energies in the range of 1-100 keV, use micro-channel plates (MCPs) to convert incident ions into a measurable current. The avalanche of electrons produced when an ion strikes the front surface of an MCP leads to a typical gain of around 103, and often a pair of matched MCPs is used to achieve gains of up to 106. For imaging applications, the electrons can either be accelerated towards a phosphor screen, and light from the phosphor registered with a fast pixel imager, or the electrons can be detected directly after the MCPs using a delay line detector or one of the new generation of CMOS-based electron detectors. Optical detection using a phosphor is currently the standard for most imaging experiments, though the decay time of the phosphor imposes a considerable limitation on the attainable time resolution in such measurements.
In any detector based on MCPs, the ‘dead’ areas between the MCP pores mean that the detection efficiency is limited to about 50%. Arrangements are available to improve the efficiency up to about 80-90%, which include various surface coatings and the use of electrostatic meshes above the MCP surface. However, the improved detection efficiency is often achieved at the cost of spatial resolution and a considerable increase in experimental complexity.
We seek to provide an improved ion detector.